A court in Estonia has convicted a former military member and his father of espionage for Russia. Ex-defense force member Deniss Metsavas, 38, and his father Pyotr Volin, 65, were suspected of treason and placed in custody by a court in Tallinn in September. Metsavas was suspected of passing state secrets and classified information to Russia’s military GRU intelligence agency for over 10 years. Metsavas was sentenced to 15.5 years behind bars and Volin was handed a six-year prison sentence on Monday, Estonia’s Harju county court said. Volin’s role was “significantly smaller,” but the court had also convicted him on two counts of unlawful handling of ammunition, court spokesman Janar Filippov said. The sentence, which includes time spent in remand prison, has not yet entered into force. Metsavas advanced to the rank of major in 2015 after service that included a posting with the NATO mission in Afghanistan, the Associated Press reported. Volin served in the Soviet military for almost a decade in the 1970s, the news agency said. Tensions between Russia and NATO member Estonia have heightened in recent years over mutual espionage accusations and the Russian annexation of the Crimean peninsula from Ukraine in 2014. The neighboring countries exchanged two men accused of espionage in 2015.